Plastic identifying method

ABSTRACT

A plastic identifying method of the present invention is provided with a step (i) of obtaining a first infrared absorption spectrum by irradiating infrared light of a predetermined wave number onto an item to be identified that contains plastic and measuring the intensity of the infrared light that is totally reflected by this item, and a step (ii) of identifying the plastic contained in the item to be identified by matching the first infrared absorption spectrum with a group of infrared absorption spectra that have been measured for predetermined materials, wherein the predetermined materials are a group of materials containing plastics, and each infrared absorption spectrum in this group of infrared absorption spectra is obtained by irradiating infrared light of a predetermined wave number onto a predetermined material, and measuring the intensity of the infrared light that is totally reflected by that material, and matching is carried out by comparing peaks in the first infrared absorption spectrum with peaks in each infrared absorption spectrum in the group of infrared absorption spectra. With this plastic identifying method, items that contain plastic can be identified accurately, even in such cases as when the items have been colored or contain additives or the like.

TECHNICAL FIELD

[0001] The present invention relates to plastic identifying methods.

BACKGROUND ART

[0002] Plastics have many strong points, such as being lightweight andstrong, capable of transparency and non-permeability to water or gases,easily colored and shaped, and due to their high usability, theirproduction volumes and usage volumes are also increasing. However,accompanying this, the volumes of discarded plastics have beenincreasing, and the increased burden on the environment has become asocial problem. To solve these problems and also to use limitedresources more effectively, there has been intensive research in recentyears on methods of recycling plastics.

[0003] Methods of recycling plastics include, for example: materialrecycling, in which plastics are repelleted and used as raw material fornew molded products; thermal recycling, in which plastics are combustedand the thermal energy recovered; and chemical recycling, in whichplastics are thermally decomposed for use as reduction agents for blastfurnaces, or decomposed down to fats/oils or monomers and reused as rawmaterials for plastics.

[0004] Among these, material recycling can be said to be the mostdesirable method, as it requires only a small amount of energy forrecycling. However, in order to prevent the recycled plastics fromhaving reduced physical properties, it is necessary to prevent themixture of different plastic types when the plastics are repelleted.Therefore, there is a need for a highly accurate method of identifyingplastics.

[0005] Conventionally, the main methods used for identifying plastictypes are spectroscopic methods such as infrared spectroscopy using nearinfrared light. However, with these spectroscopic methods,identification is difficult when the plastics to be identified aredark-coloured plastics (for example, the plastics used for such items asthe chassis of television receivers and many other household electricalappliances are colored black), because of reasons such as the appliednear infrared light being absorbed, and it is therefore difficult toobtain infrared absorption spectra.

[0006] Furthermore, when identifying plastic types using obtainedinfrared absorption spectra, it is usual to compare and match theobtained infrared absorption spectra with a group of infrared absorptionspectra of various standard plastics. The process of comparing andmatching involves searching for the infrared absorption spectrum of astandard plastic that is the best fit with the obtained infraredabsorption spectrum, and thereby identifying the type of plastic.

[0007] Very often plastics that are to be recycled contain flameretardants and other additives. However, the standard plastics that havebeen compared and matched are basically “pure” polymers, and plasticsthat contain additives have not been included as objects of comparisonand matching. Furthermore, the data for the infrared absorption spectraof standard plastics usually have been data obtained by penetratinginfrared light through the items to be identified (penetration method).

DISCLOSURE OF INVENTION

[0008] In view of these circumstances, it is an object of the presentinvention to provide a plastic identifying method that enables plasticsto be identified accurately, even in such cases as when the items to beidentified have been colored or contain additives or the like.

[0009] To achieve this object, the plastic identifying method of thepresent invention includes:

[0010] (i) a step of obtaining a first infrared absorption spectrum byirradiating infrared light of a predetermined wave number onto an itemto be identified that contains plastic and measuring the intensity ofthe infrared light that is totally reflected by this item, and;

[0011] (ii) a step of identifying the plastic contained in the item tobe identified by matching the first infrared absorption spectrum with agroup of infrared absorption spectra that have been measured for a groupof predetermined materials,

[0012] wherein the group of predetermined materials is a group ofmaterials containing plastics, and each infrared absorption spectrum inthe group of infrared absorption spectra is obtained by irradiatinginfrared light of a predetermined wave number onto each materialincluded in the group of predetermined materials, and measuring theintensity of the infrared light that is totally reflected by thatmaterial,

[0013] and matching is carried out by comparing peaks in the firstinfrared absorption spectrum with peaks in each infrared absorptionspectrum in the group of infrared absorption spectra.

[0014] The step (i) of the plastic identifying method also may include:

[0015] (i-a) a step of sampling a test piece from the item to beidentified; and

[0016] (i-b) a step of obtaining the first infrared absorption spectrumby irradiating infrared light of a predetermined wave number onto thetest piece, and measuring the intensity of the infrared light that istotally reflected by the test piece.

[0017] The step (i) of the plastic identifying method also may include:

[0018] (i-A) a step of sampling a test piece from the item to beidentified;

[0019] (i-B) a step of obtaining a second infrared absorption spectrumby irradiating infrared light of a predetermined wave number onto afirst face of the test piece that corresponds to a surface of the itemto be identified, and measuring the intensity of the infrared light thatis totally reflected by the first face, and

[0020] (i-C) a step of obtaining the first infrared absorption spectrumby irradiating infrared light of a predetermined wave number onto asecond face of the test piece that was first exposed when the test piecewas sampled, and measuring the intensity of the infrared light that istotally reflected by the second face.

[0021] The predetermined group of materials in the plastic identifyingmethod may be a group of materials that contains at least one materialselected from the group consisting of acrylonitrile-butadiene-styrenecopolymers, polypropylenes, and polystyrenes.

[0022] The predetermined group of materials in the plastic identifyingmethod may be a group of materials containing plastics that containflame retardants.

[0023] The plastics that contain flame retardants in the plasticidentifying method may be acrylonitrile-butadiene-styrene copolymersthat contain tetrabromobisphenol A (TBA) series flame retardants.

[0024] The plastics that contain flame retardants in the plasticidentifying method may be polystyrenes that contain at least one of theflame retardants selected from the group consisting of decabrominatedflame retardants, TBA series flame retardants, triazine series flameretardants, and ethylenebis series flame retardants.

[0025] In the step (ii) of the plastic identifying method, when thefirst infrared absorption spectrum has a peak in the wave number rangeof 906 cm⁻¹ to 914 cm⁻¹, the wave number range of 1,023 cm⁻¹ to 1,031cm⁻¹, and the wave number range of 2,234 cm⁻¹ to 2,242 cm⁻¹, and thevalue obtained by dividing the highest peak intensity in the wave numberrange of 1,000 cm⁻¹ to 1,008 cm⁻¹ by the highest peak intensity in thewave number range of 1023 cm⁻¹ to 1,031 cm⁻¹ is not greater than 0.5,then the item to be identified may be identified as anacrylonitrile-butadiene-styrene copolymer.

[0026] In the step (ii) of the plastic identifying method, when thefirst infrared absorption spectrum has a peak in the wave number rangeof 1,373 cm⁻¹ to 1,381 cm⁻¹, the wave number range of 2,913 cm⁻¹ to2,921 cm⁻¹, and the wave number range of 2,946 cm⁻¹ to 2,954 cm⁻¹, thenthe item to be identified can be identified as a polypropylene.

[0027] In the step (ii) of the plastic identifying method, when thefirst spectrum has a peak in the wave number range of 1,368 cm⁻¹ to1,376 cm⁻¹ and the wave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹, andthe value obtained by dividing the intensity of the highest peak in thewave number range of 1,000 cm⁻¹ to 1,008 cm⁻¹ by the intensity of thehighest peak in the wave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹ is notgreater than 0.5, then the item to be identified can be identified as apolystyrene that does not contain a TBA series flame retardant.

[0028] In the step (ii) of the plastic identifying method, when thefirst spectrum has a peak in the wave number range of 1,368 cm⁻¹ to1,376 cm⁻¹ and the wave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹, anddoes not have a peak in the wave number range of 1,348 cm⁻¹ to 1,356cm⁻¹, and the value obtained by dividing the intensity of the highestpeak in the wave number range of 1,000 cm⁻¹ to 1,008 cm⁻¹ by theintensity of the highest peak in the wave number range of 1,023 cm⁻¹ to1,031 cm⁻¹ is not greater than 0.5, then the item to be identified canbe identified as a polystyrene that does not contain a flame retardant.

[0029] In the step (ii) of the plastic identifying method, when thefirst spectrum has a peak in the wave number range of 1,349 cm⁻¹ to1,357 cm⁻¹ and the wave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹, anddoes not have a peak in the wave number range of 907 cm⁻¹ to 915 cm⁻¹,and the value obtained by dividing the intensity of the highest peak inthe wave number range of 1,000 cm⁻¹ to 1,008 cm⁻¹ by the intensity ofthe highest peak in the wave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹ isnot greater than 0.5, then the item to be identified can be identifiedas a polystyrene that contains decabrominated flame retardant.

[0030] In the step (ii) of the plastic identifying method, when thefirst spectrum has a peak in the wave number range of 1,000 cm⁻¹ to1,008 cm⁻¹ and the wave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹, andthe value obtained by dividing the intensity of the highest peak in thewave number range of 1,000 cm⁻¹ to 1,008 cm⁻¹ by the intensity of thehighest peak in the wave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹ is atleast 0.5, then the item to be identified can be identified as apolystyrene that contains a TBA series flame retardant.

[0031] In the step (ii) of the plastic identifying method, when thefirst spectrum has a peak in the wave number range of 1,356 cm⁻¹ to1,364 cm⁻¹, the wave number range of 1,227 cm⁻¹ to 1,235 cm⁻¹, the wavenumber range of 1,085 cm⁻¹ to 1,093 cm⁻¹, and the wave number range of1,023 cm⁻¹ to 1,031 cm⁻¹, and the value obtained by dividing theintensity of the highest peak in the wave number range of 1,000cm⁻¹ to1,008 cm⁻¹ by the intensity of the highest peak in the wave number rangeof 1,023 cm⁻¹ to 1,031 cm⁻¹ is not greater than 0.5, then the item to beidentified can be identified as a polystyrene that contains a triazineseries flame retardant.

[0032] In the step (ii) of the plastic identifying method, when thefirst spectrum has a peak in the wave number range of 1,369 cm⁻¹ to1,377 cm⁻¹, the wave number range of 1,137 cm⁻¹ to 1,145 cm⁻¹, the wavenumber range of 742 cm⁻¹ to 750 cm⁻¹, and the wave number range of 1,023cm⁻¹ to 1,031 cm⁻¹, and the value obtained by dividing the intensity ofthe highest peak in the wave number range of 1,000 cm⁻¹ to 1,008 cm⁻¹ bythe intensity of the highest peak in the wave number range of 1,023 cm⁻¹to 1,031 cm⁻¹ is not greater than 0.5, then the item to be identifiedcan be identified as a polystyrene that contains an ethylenebis seriesflame retardant.

[0033] After the step (ii), the plastic identifying method further mayinclude:

[0034] (x) a step of obtaining a third infrared absorption spectrum byexcluding from the peaks of the first infrared absorption spectrum thepeaks of the infrared absorption spectrum of any plastic identified ascontained in the item to be identified, and

[0035] (y) a step of identifying a substance that is adhering to asurface of the item to be identified by matching the third infraredabsorption spectrum with the group of infrared absorption spectra.

[0036] The above-mentioned adhering substances may be substances thatcontain at least one material selected from the group consisting offats/oils, proteins, coatings, celluloses, and inorganic silicates.

[0037] In the step (y) of the plastic identifying method, when the thirdinfrared absorption spectrum has a peak in the wave number range of1,736 cm⁻¹ to 1,744 cm⁻¹, then the adhering substance can be identifiedas at least one material selected from the group consisting of fats/oilsand coatings.

[0038] In the step (y) of the plastic identifying method, when the thirdinfrared absorption spectrum has a peak in the wave number range of1,646 cm⁻¹ to 1,654 cm⁻¹ and the wave number range of 1,541 cm⁻¹ to1,549 cm⁻¹, then the adhering substance can be identified as a protein.

[0039] In the step (y) of the plastic identifying method, when the thirdinfrared absorption spectrum has a peak in the wave number range of1,000 cm⁻¹ to 1,100 cm⁻¹, then the adhering substance can be identifiedas at least one material selected from the group consisting ofcelluloses and inorganic silicates.

[0040] After the step (i), the plastic identifying method further mayinclude:

[0041] (X) a step of obtaining a fourth infrared absorption spectrum byexcluding the peaks of the first infrared absorption spectrum from thepeaks of the second infrared absorption spectrum, and

[0042] (Y) a step of identifying a substance that is adhering to asurface of the item to be identified by matching the fourth infraredabsorption spectrum with the group of infrared absorption spectra.

[0043] After the step (i), the plastic identifying method may furtherinclude:

[0044] (s) a step of determining an area D₁ of the peaks in the firstinfrared absorption spectrum in the wave number range of 400 cm⁻¹ to7,000 cm⁻¹,

[0045] (t) a step of determining an area D₂ of the peaks in the secondinfrared absorption spectrum in the wave number range of 400 cm⁻¹ to7,000 cm⁻¹, and

[0046] (u) a step of determining a value D by dividing the area D₂ bythe area D₁ (D=D₂/D₁).

[0047] After the step (ii), the plastic identifying method further mayinclude:

[0048] (S) a step of establishing a first baseline of the first infraredabsorption spectrum by joining with a straight line a peak in the firstinfrared absorption spectrum in the vicinity of the wave number 2,750cm⁻¹ with a peak in the vicinity of the wave number 3,140 cm⁻¹,

[0049] (T) a step of establishing a second baseline of the firstinfrared absorption spectrum by joining with a straight line a peak inthe first infrared absorption spectrum in the vicinity of the wavenumber 3,663 cm⁻¹ with a peak in the vicinity of the wave number 3,791cm⁻¹, and

[0050] (U) a step of taking the peak intensity in the first infraredabsorption spectrum in the vicinity of the wave number 2,920 cm⁻¹ as H₁and the peak intensity in the vicinity of the wave number 3,750 cm⁻¹ asH₂, and determining a value H by dividing the H₂ by the H₁. Note thatthe H₁ is the peak intensity of the first infrared absorption spectrumrelative to the first baseline, and that the H₂ is the peak intensity ofthe first infrared absorption spectrum relative to the second baseline.

BRIEF DESCRIPTION OF DRAWINGS

[0051]FIG. 1 is a cross-sectional view showing an example of a detectionunit that can implement the plastic identifying method of the presentinvention.

[0052]FIG. 2 is a schematic drawing showing an example of anidentification apparatus that can implement the plastic identifyingmethod of the present invention.

[0053]FIG. 3 shows an example of an infrared absorption spectrummeasured using the plastic identifying method of the present invention.

[0054]FIG. 4 shows another example of an infrared absorption spectrummeasured using the plastic identifying method of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0055] Referring to the accompanying drawings, the following is anexplanation of embodiments of the present invention. It should be notedthat in the following embodiments, the same components are referred toby the same reference numerals, and duplicate explanations are sometimesomitted.

[0056] Embodiment 1

[0057] The plastic identifying method of the present invention includes:

[0058] (i) a step of obtaining a first infrared absorption spectrum byirradiating infrared light of a predetermined wave number onto an itemto be identified that contains plastic and measuring the intensity ofthe infrared light that is totally reflected by this item, and;

[0059] (ii) a step of identifying the plastic contained in the item tobe identified by matching the first infrared absorption spectrum with agroup of infrared absorption spectra that have been measured for a groupof predetermined materials.

[0060] The group of predetermined materials mentioned above is a groupof materials containing plastics. Each infrared absorption spectrum inthis group of infrared absorption spectra is obtained by irradiatinginfrared light of a predetermined wave number onto each materialincluded in the group of predetermined materials, and measuring theintensity of the infrared light that is totally reflected by thatmaterial. Matching is then carried out by comparing peaks in the firstinfrared absorption spectrum with peaks in each infrared absorptionspectrum in the group of infrared absorption spectra.

[0061] With the plastic identifying method, the plastic contained in anitem to be identified can be identified with very good accuracy, evenwhen the item to be identified has been colored, or even when the itemto be identified contains a flame retardant.

[0062] There is no particular limitation to the method of carrying outthe step (i) in the plastic identifying method. For example, a detectionunit combining items such as an infrared light source, lenses, a prism,and a detection device may be used. An example of such a detection unitis shown in FIG. 1. It should be noted that the above-mentioned infraredlight of a predetermined wave number (also referred to below as simply“infrared light”) has a wave number in the range, for example, of 400cm⁻¹ to 7,000 cm⁻¹ (which puts this light mainly into the category ofmid-infrared light).

[0063] Shown in FIG. 1, a detection unit 1 is provided with a lightsource 2, a prism 3, and a detection device 4. Infrared light 6 emittedfrom the light source 2 is irradiated onto the item 5 to be identifiedby the prism 3. At this time, the incident light angle θ, which is shownin FIG. 1, should be set so as the infrared light 6 to be totallyreflected by the surface of the item 5 to be identified. (The incidentlight angle θ should be greater than the critical angle of totalreflectance for the infrared light 6). For example, the incident lightangle θ may be set in the range of 30° to 85°. The intensity of theinfrared light 6 that is totally reflected by the surface of the item 5to be identified is measured by the detection device 4 after passingthrough the prism 3. It should be noted that FIG. 1 is a cross-sectionalview in which hatching has been omitted in order to make the drawingeasier to view.

[0064] Additionally, an ATR (attenuated total reflectance) method may beused as the method for causing total reflectance of infrared light fromthe surface of the item to be identified. In this measurement method,the infrared light absorption spectrum (“infrared light absorptionspectrum” is also referred to hereinafter as simply “spectrum”) can beobtained by using an ATR prism, which is a medium with a high refractiveindex, irradiating infrared light onto the surface of the item to beidentified at an angle greater than the critical angle, and measuringthe intensity of the totally reflected infrared light.

[0065] By using methods of totally reflecting infrared light from thesurface of the item to be identified, the type of plastic contained inthe item to be identified can be accurately identified even when theitem to be identified has been colored.

[0066] There is no particular limitation to the method of carrying outthe step (ii) in this identifying method. For example, it may involvefirst setting up a database or the like that records in advance themeasured spectra of a predetermined group of materials, then matchingthem successively with the first spectrum obtained in the step (i). Thepredetermined group of materials should be a group of materials thatcontains plastic. Additionally, it is possible to use the same method asthat described above in the step (i) for measuring the spectra ofpredetermined groups of materials.

[0067] Matching should be performed by comparing the peaks of thespectra that are to be contrasted. It is possible to compare the peaks,for example, in terms of peak position or peak intensity. This methodmay involve, for example, verifying whether or not a specific spectralpeak of one of the above-mentioned spectra is present in the firstspectrum, or by verifying the spectrum (differential spectrum) obtainedby taking the difference between the spectra that are to be contrasted(if no peak is apparent in the differential spectrum, the two spectra tobe contrasted can be considered approximately equivalent). As items tobe identified for recycling exhibit various conditions of degradation,it is preferable to have a method that verifies whether or not aspecific spectral peak is present in the first spectrum. The result ofthis matching is that, of the group of predetermined materials, thematerial exhibiting the spectrum best approximating the first spectrumcan be taken as the type of plastic of the item to be identified.

[0068] The step (i) in the identifying method of the present inventionmay include:

[0069] (i-a) a step of sampling a test piece from the item to beidentified, and

[0070] (i-b) a step of obtaining the first infrared absorption spectrumby irradiating infrared light of a predetermined wave number onto thetest piece, and measuring the intensity of the infrared light that istotally reflected by the test piece.

[0071] In an identifying method such as this, infrared light is notirradiated directly onto the item to be identified, but rather infraredlight is irradiated onto a test piece that has been sampled from theitem. For this reason, even when the actual item to be identified isvery large, the identification process is simple. Furthermore, as thesize and shape of the test pieces can be optimized to suit the detectionunit regardless of the shape of the actual items to be identified,plastic types contained in the items to be identified can be identifiedaccurately and consistently. This identifying method is also suitablefor continuous identifying processes.

[0072] Moreover, the step (i) in the identifying method of the presentinvention may include:

[0073] (i-A) a step of sampling a test piece from the item to beidentified,

[0074] (i-B) a step of obtaining a second infrared absorption spectrumby irradiating infrared light of a predetermined wave number onto afirst face of the test piece that corresponds to a surface of the itemto be identified, and measuring the intensity of the infrared light thatis totally reflected by the first area, and

[0075] (i-C) a step of obtaining a first infrared absorption spectrum byirradiating infrared light of a predetermined wave number onto a secondface of the test piece that was first exposed when the test piece wassampled, and measuring the intensity of the infrared light that istotally reflected by the second face.

[0076] In an identifying method such as this, spectral measurements areperformed for at least two faces of the test pieces. Furthermore, one ofthe measured faces is a surface that was first exposed at the time ofsampling. For this reason, the type of plastic contained in the item tobe identified can be identified accurately and consistently even whenthe surface of the item to be identified has degraded due to use over along period and even when grime and similar substances are adhering tothe surface of the item to be identified. Additionally, as will beexplained below, using this identifying method makes it possible toquantify the extent of dirt on the surface of items to be identified.

[0077] The identifying method can be implemented, for example, by usingthe identifying apparatus shown in FIG. 2. The identifying apparatusshown in FIG. 2 is provided with a sampling unit 8 that samples a testpiece 7 from the item 12 to be identified, an identification unit 9 thatis provided with a detection unit 1 for identifying the type of plasticcontained in the test piece 7, and a transport unit 10 that transportsthe test piece from the sampling unit 8 to the detection unit 1.

[0078] The sampling unit 8 may be provided with, for example, a punchpress. In this case, it is easy to sample the test piece 1. Theidentification unit 9 may be provided with, for example, the detectionunit shown in FIG. 1. The transport unit 10 may be provided with, forexample, a chucking unit 11. When the chucking unit 11 is provided, itis easier to measure the surfaces for two or more surfaces of the testpiece 1. Additionally, the matching of the first spectrum with a groupof spectra may be performed using the identification unit 9. In thiscase, the data for the group of spectra may be recorded in advance inthe identification unit 9, then after the first spectrum is measured bythe detection unit 4, the first spectrum data can be sent to theidentification unit 9 and matched.

[0079] In the identifying method of the present invention, thepredetermined group of materials may be the group of materials thatcontains at least one material selected from the group consisting ofacrylonitrile-butadiene-styrene copolymer (ABS), polypropylene (PP), andpolystyrene (PS). These plastics are very often used in the chassis ofhousehold electrical appliances and the like.

[0080] In the identifying method of the present invention, thepredetermined group of materials may be a group of materials containingplastic that contains a flame retardant. In fact, the plastic containedin items to be identified for recycling very often contains flameretardants. When the plastic contained in an item to be identifiedcontains flame retardants, it is sometimes difficult to identify theplastic type merely by matching the first measured spectrum with a groupof spectra of standard plastics. For that purpose, with an identifyingmethod such as this, even when the item to be identified contains flameretardants, the type of plastic contained in item to be identified canbe identified accurately.

[0081] In the identifying method, plastics that contain flame retardantsmay be an ABS that contains a tetrabromobisphenol A (TBA) series flameretardant. Moreover, the plastics that contain flame retardants may be aPS that contains at least one type of the flame retardant selected fromthe group consisting of decabrominated flame retardants, TBA seriesflame retardants, triazine series flame retardants, and ethylenebisseries flame retardants. These plastics are very often used in thechassis of household electrical appliances and the like.

[0082] In the step (ii) in the identifying method of the presentinvention, when the first infrared absorption spectrum has a peak in thewave number range of 906 cm⁻¹ to 914 cm⁻¹, the wave number range of1,023 cm⁻¹ to 1,031 cm⁻¹, and the wave number range of 2,234 cm⁻¹ to2,242 cm⁻¹, and the value obtained by dividing the highest peakintensity in the wave number range of 1,000 cm⁻¹ to 1,008 cm⁻¹ by thehighest peak intensity in the wave number range of 1,023 cm⁻¹ to 1,031cm⁻¹ is not greater than 0.5, then the item to be identified may beidentified as an ABS. It should be noted that the reason for allowingsome width in the peak wave numbers used for identification is due toconsideration for the effects of such factors as measurement error andpeak shifts caused by additives, and the like.

[0083] Table 1 below shows a compilation of the ABS identifying method.The R value in Table 1 is the value obtained by dividing the highestpeak intensity in the wave number range of 1,000 cm⁻¹ to 1,008 cm⁻¹ bythe highest peak intensity in the wave number range of 1,023 cm⁻¹ to1,031 cm⁻¹. It should be noted that the R values in this specificationall indicate this value. TABLE 1 Plastic type Range of wave number(cm⁻¹) used to be identified for identification and peak yes/no R valueABS   906 to 914: yes R ≦ 0.5 1,023 to 1,031: yes 2,234 to 2,242: yes

[0084] In the step (ii) in the identifying method of the presentinvention, identification may be performed as shown in Table 2 below.The format of Table 2 is the same as Table 1 above. Specifically, forexample, when the first infrared absorption spectrum in the step (ii)has a peak in the wave number range of 1,373 cm⁻¹ to 1,381 cm⁻¹, thewave number range of 2,913 cm⁻¹ to 2,921 cm⁻¹, and the wave number rangeof 2,946 cm⁻¹ to 2,954 cm⁻¹, then the item to be identified can beidentified as a PP. It should be noted that the identifying method forABS shown in Table 1 is also listed in Table 2. TABLE 2 Range of wavenumber Plastic type (cm⁻¹) used for identification to be identified andpeak yes/no R value ABS   906 to 914: yes R ≦ 0.5 1,023 to 1,031: yes2,234 to 2,242: yes PP 1,373 to 1,381: yes Not used in 2,913 to 2,921:yes identification 2,946 to 2,954: yes PS (not containing TBA 1,368 to1,376: yes R ≦ 0.5 series flame retardants) 1,023 to 1,031: yes PS (notcontaining flame 1,368 to 1,376: yes R ≦ 0.5 retardants) 1,023 to 1,031:yes 1,348 to 1,356: no PS (containing 1,349 to 1,357: yes R ≦ 0.5decabrominated flame 1,023 to 1,031: yes retardants)   907 to 915: no PS(containing TBA series 1,000 to 1,008: yes R ≧ 0.5 flame retardants)1,023 to 1,031: yes PS (containing triazine 1,356 to 1,364: yes R ≦ 0.5series flame retardants) 1,227 to 1,235: yes 1,085 to 1,093: yes 1,023to 1,031: yes PS (containing ethylenebis 1,369 to 1,377: yes R ≦ 0.5series flame retardants) 1,137 to 1,145: yes   742 to 750: yes 1,023 to1,031: yes

[0085] The following is an explanation of the value R. As ABS and PS areplastics that contain styrene, they have a peak in the vicinity of thewave number 1,027 cm⁻¹. On the other hand, ABS and PS sometimes containTBA series flame retardants as additives, and when they contain a TBAseries flame retardant, a peak appears in the vicinity of the wavenumber 1,004 cm⁻¹. However, even when they do not contain a TBA seriesflame retardant, a peak sometimes appears in the vicinity of the wavenumber 1,004 cm⁻¹ due to such factors as the other substances containedin items to be identified and measurement error, and therefore it is notalways possible to be certain whether a plastic contains TBA seriesflame retardants or not based on only whether there is a peak in thevicinity of the wave number 1,004 cm⁻¹. It is for this reason that, inthe identifying method of the present invention, the value R isdetermined, which is the ratio of the highest peak intensity in the wavenumber range of 1,000 cm⁻¹ to 1,008 cm⁻¹ with the highest peak intensityin the wave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹. This method makesit possible to identify whether ABS or PS materials contain TBA seriesflame retardants reliably.

[0086] The following is an explanation with a specific example of howthe first spectrum measured for the item to be identified and the groupof spectra are matched.

[0087] The spectra shown in FIGS. 3 and 4 are each a first spectrum fordifferent items to be identified obtained by carrying out the step (i).

[0088] The spectrum shown in FIG. 3 has peaks at the wave number 1,027cm⁻¹ and the wave number 1,004 cm⁻¹ (shown as peak 3-1 and peak 3-2 inFIG. 3). Furthermore, the value obtained by dividing the intensity ofthe highest peak in the wave number range of 1,000 cm⁻¹ to 1,008 cm⁻¹(that is, peak 3-2) by the intensity of the highest peak in the wavenumber range of 1,023 cm⁻¹ to 1,031 cm⁻¹ (that is, peak 3-1) isapproximately 0.8. Therefore, the item to be identified, whose measuredspectrum is shown in FIG. 3, can be identified as a PS containing a TBAseries flame retardant. It should be noted that, in the spectrum shownin FIG. 3, the horizontal axis is the infrared light wave number (cm⁻¹)and the vertical axis is light absorbance.

[0089] Next, the spectrum shown in FIG. 4 has peaks at the wave number1,372 cm⁻¹ and the wave number 1,027 cm⁻¹ (shown as peak 4-1 and peak4-2 in FIG. 4). Furthermore, the value obtained by dividing theintensity of the highest peak in the wave number range of 1,000 cm⁻¹ to1,008 cm⁻¹ (that is, peak 4-3 in FIG. 4) by the intensity of the highestpeak in the wave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹ (that is, peak4-2) is approximately 0.3. Therefore, the item to be identified, whosemeasured spectrum is shown in FIG. 4, can be identified as a PS notcontaining a TBA series flame retardant. It should be noted that, in thespectrum shown in FIG. 4, the horizontal axis is the infrared light wavenumber (cm⁻¹) and the vertical axis is light absorbance.

[0090] Embodiment 2

[0091] The following is an explanation of an example of an embodiment ofthe plastic identifying method of the present invention in which an itemthat has a substance adhering to its surface is identified.

[0092] After the step (ii), the identifying method of the presentinvention may further include:

[0093] (x) a step of obtaining a third infrared absorption spectrum byexcluding from the peaks of the first infrared absorption spectrum thepeaks of the infrared absorption spectrum of any plastic identified ascontained in the item to be identified, and

[0094] (y) a step of identifying a substance that is adhering to asurface of the item to be identified by matching the third infraredabsorption spectrum with the group of infrared absorption spectra.

[0095] It is often the case that an item to be identified for recyclinghas various substances adhering to its surface, but with an identifyingmethod such as this, it is possible to identify the substances that areadhering to the surface of the item to be identified.

[0096] There is no particular limitation to the method of obtaining thethird spectrum in the step (x). For example, the differential spectrummay be obtained by subtracting from the first spectrum the spectrum ofany plastic identified as included in the items to be identified.Furthermore, the matching of the third spectrum with the group ofinfrared absorption spectra can be the same matching method as thatdescribed in the first embodiment.

[0097] Moreover, the step (i) in the identifying method of the presentinvention may include:

[0098] (i-A) a step of sampling a test piece from the item to beidentified,

[0099] (i-B) a step of obtaining a second infrared absorption spectrumby irradiating infrared light of a predetermined wave number onto afirst face of the test piece that corresponds to the surface of the itemto be identified, and measuring the intensity of the infrared light thatis totally reflected by the first face, and

[0100] (i-C) a step of obtaining the first infrared absorption spectrumby irradiating infrared light of a predetermined wave number onto asecond face of the test piece that was first exposed when the piece wassampled, and measuring the intensity of the infrared light that istotally reflected by the second face, and after the step (i), it furthermay include:

[0101] (X) a step of obtaining a fourth infrared absorption spectrum byexcluding the peaks of the first infrared absorption spectrum from thepeaks of the second infrared absorption spectrum, and

[0102] (Y) a step of identifying a substance that is adhering to asurface of the item to be identified by matching the fourth infraredabsorption spectrum with the group of infrared absorption spectra.

[0103] When a substance adheres to the surface of an item to beidentified, the second spectrum can be considered to contain thespectrum of the substance, because the substance remains on the firstface of the test piece sampled from the item to be identified. On theother hand, it can be assumed that no substance will be present on thesecond face, which is first exposed during sampling. Therefore, with anidentifying method such as this, it is possible to identify thesubstances that are present on the surface of the item to be identified.

[0104] There is no particular limitation to the method for obtaining thefourth spectrum in the step (X). For example, the differential spectrummay be obtained by subtracting the first spectrum from the secondspectrum. Furthermore, the matching of the fourth spectrum with thegroup of infrared absorption spectra that occurs in the step (Y) may bethe same matching method as that described in the first embodiment.Likewise, the step (i) also may be the same method as that described inthe first embodiment.

[0105] In the identifying method of the present invention, theabove-mentioned substance may be one material selected from the groupconsisting of fats/oils, proteins, coatings, celluloses, and inorganicsilicates. Such materials often adhere to items to be identified forrecycling. It should be noted that acrylic resin-based protective films,for example, or similar materials used to protect the surfaces of itemsto be identified can be considered as coatings. Additionally, examplesof proteins include hand grime and the like, examples of cellulosesinclude lint and the like, and examples of inorganic silicates includedust.

[0106] The step (y) (and the step (Y)) in the identifying method of thepresent invention may be performed as shown in Table 3 below. The formatof Table 3 is the same as Table 1 and Table 2 above. Note though, thatthe value R is not used in identifying the adhering substances. Forexample, when the third (or fourth) infrared absorption spectrum in thestep (y) (or the step (Y)) has a peak in the wave number range of 1,736cm⁻¹ to 1,744 cm⁻¹, the adhering substance can be identified as being atleast one material of the group consisting of fats/oils and coatings.TABLE 3 Type of adhering material Range of wave number (cm⁻¹) used to beidentified for identification and peak yes/no At least one selected fromfats/oils 1,736 to 1,744: yes and coatings Proteins 1,646 to 1,654: yes1,541 to 1,549: yes At least one selected from 1,000 to 1,100: yescelluloses and inorganic silicates

[0107] Embodiment 3

[0108] The following is an explanation of an example of an embodiment ofthe plastic identifying method of the present invention in which theextent of dirt on the surface of an item to be identified is quantified.

[0109] The step (i) in the identifying method of the present inventionmay include:

[0110] (i-A) a step of sampling a test piece from an item to beidentified,

[0111] (i-B) a step of obtaining a second infrared absorption spectrumby irradiating infrared light of a predetermined wave number onto afirst face of the test piece that corresponds to a surface of the itemto be identified, and measuring the intensity of the infrared light thatis totally reflected by the first face, and

[0112] (i-C) a step of obtaining the first infrared absorption spectrumby irradiating infrared light of a predetermined wave number onto asecond face of the test piece that was first exposed when the piece wassampled, and measuring the intensity of the infrared light that istotally reflected by the second face, and it may further include:

[0113] (s) a step of determining an area D₁ of the peaks in the firstinfrared absorption spectrum in the wave number range of 400 cm⁻¹ to7,000 cm⁻¹,

[0114] (t) a step of determining an area D₂ of the peaks in the secondinfrared absorption spectrum in the wave number range of 400 cm⁻¹ to7,000 cm⁻¹, and

[0115] (u) a step of determining a value D by dividing the area D₂ bythe area D₁ (D=D₂/D₁).

[0116] An item to be identified that has been recovered from themarketplace sometimes has dirt adhering to its surface. In cases whendirt is adhering in this way, reliable spectra cannot be obtained simplyby measuring the spectrum of the item to be identified, and sometimes itis difficult to identify the type of plastic contained in the item.Therefore, by sampling a test piece from the item to be identified andmeasuring the spectra of a first face that corresponds to its surface(which is considered to have dirt adhering) and a second face that wasfirst exposed at the time of sampling (considered not to have dirtadhering), and by quantifying the difference of the peak areas of theirrespective spectra, or specifically, determining the ratio of their peakareas, it is possible to quantify the extent of dirt adhering to thesurface of the item to be identified (a coefficient of surface soiling).If the extent of dirt adhering to the surface of an item to beidentified can be quantified, it is possible to identify with greateraccuracy the type of plastic it contains. With the obtained coefficientof surface soiling value D, it is possible to perform processes such asremoving an item from those targeted for recycling (for example, when Dis equal to or less than 0.5).

[0117] It should be noted that there are no particular limitations tothe methods for performing the steps (s), (t), and (u). For example,mathematical processing may be performed for each obtained spectrum.Additionally, the step (i) may also be the same method as that describedin the first embodiment.

[0118] Embodiment 4

[0119] The following is an explanation of an example of an embodiment ofthe present invention that involves a method for verifying whether areliable spectrum has been obtained or not when a spectrum is obtainedfrom an item to be identified.

[0120] After the step (ii), the identifying method of the presentinvention may further include:

[0121] (S) a step of establishing a first baseline of the first infraredabsorption spectrum by joining with a straight line a peak in the firstinfrared absorption spectrum in the vicinity of the wave number 2,750cm⁻¹ with a peak in the vicinity of the wave number 3,140 cm⁻¹,

[0122] (T) a step of establishing a second baseline of the firstinfrared absorption spectrum by joining with a straight line a peak inthe first infrared absorption spectrum in the vicinity of the wavenumber 3,663 cm⁻¹ with a peak in the vicinity of the wave number 3,791cm⁻¹, and

[0123] (U) a step of taking the peak intensity in the first infraredabsorption spectrum in the vicinity of the wave number 2,920 cm⁻¹ as H₁and the peak intensity in the vicinity of the wave number 3,750 cm⁻¹ asH₂, and determining a value H by dividing the H₂ by the H₁. Note thatthe H₁ is the peak intensity of the first infrared absorption spectrumrelative to the first baseline, and that the H₂ is the peak intensity ofthe first infrared absorption spectrum relative to the second baseline.

[0124] A peak in the vicinity of the wave number 2,750 cm⁻¹ here means apeak around the wave number 2,750 cm⁻¹, including a range of ±4 cm⁻¹.Additionally, peak refers to the peak of the highest intensity in caseswhen there are multiple peaks within this range. The same judgementshould also be performed for the peaks measured at other vicinities ofwave number in the steps (S), (T), and (U).

[0125] When measuring the infrared absorption spectra of an item to beidentified, very accurate identification of the type of plasticcontained in the item can be achieved if reliable contact is madebetween the detection unit, which irradiates onto the item to beidentified and measures the intensity of the infrared light that istotally reflected by the surface of the item to be identified, and theitem to be identified. For this reason, there is a need for a methodthat verifies whether the detection unit and the item to be identifiedare reliably in contact.

[0126] When contact between the item to be identified and the detectionunit is incomplete, there is a layer of air between them. Because watervapor is contained in this layer of air, the condition of the contactbetween the item to be identified and the detection unit can be verifiedby analyzing the extent to which the spectrum of water vapor iscontained in the spectrum measured for the item to be identified.

[0127] Therefore, by dividing H₂, the intensity of the peak in thevicinity of the wave number 3,750 cm⁻¹, which corresponds to that ofwater vapor, by H₁, the intensity of the peak in the vicinity of thewave number 2,920 cm⁻¹, which is a reference for resin identification,and thereby obtaining the value H, it is possible to verify thecondition of the contact between the item to be identified and thedetection unit. For example, if the value H is at least 0.3, the peakintensity of the water vapor can be diagnosed as high, and the contactbetween the item to be identified and the detection unit can bediagnosed as incomplete. In this case, the position of the item to beidentified can be adjusted and measurements retaken. Furthermore, if thevalue H is lower than 0.3, the process may proceed to identify the typeof plastic contained in the item to be identified.

[0128] It should be noted that there is no particular limitation to themethod for performing the steps (S), (T), and (U). For example,mathematical processing may be performed for each obtained spectrum.

[0129] The present invention may be embodied in other specific formswithout departing from the spirit or essential characteristics thereof.The embodiments disclosed in this application are to be considered inall respects as illustrative and not restrictive, the scope of theinvention being indicated by the appended claims rather than by theforegoing description. All changes that come within the meaning andrange of equivalency of the claims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

[0130] As shown above, with the plastic identifying method of thepresent invention, the type of plastic contained in an item can beidentified accurately even when the item to be identified has beencolored or contains additives or the like.

1. A plastic identifying method comprising: (i) a step of obtaining afirst infrared absorption spectrum by irradiating infrared light of apredetermined wave number onto an item to be identified that containsplastic and measuring the intensity of the infrared light that istotally reflected by the item; and (ii) a step of identifying theplastic contained in the item to be identified by matching the firstinfrared absorption spectrum with a group of infrared absorption spectrathat have been measured for a predetermined group of materials; whereinthe predetermined group of materials is a group of materials containingplastics; and each infrared absorption spectrum in the group of infraredabsorption spectra is obtained by irradiating infrared light of apredetermined wave number onto each material included in the group ofpredetermined materials, and measuring the intensity of the infraredlight that is totally reflected by the material; and matching is carriedout by comparing peaks in the first infrared absorption spectrum withpeaks in each infrared absorption spectrum in the group of infraredabsorption spectra.
 2. The plastic identifying method according to claim1, wherein the step (i) comprises: (i-a) a step of sampling a test piecefrom the item to be identified; and (i-b) a step of obtaining the firstinfrared absorption spectrum by irradiating infrared light of apredetermined wave number onto the test piece, and measuring theintensity of the infrared light that is totally reflected by the testpiece.
 3. The plastic identifying method according to claim 1, whereinthe step (i) comprises: (i-A) a step of sampling a test piece from theitem to be identified; (i-B) a step of obtaining a second infraredabsorption spectrum by irradiating infrared light of a predeterminedwave number onto a first face of the test piece that corresponds to asurface of the item to be identified, and measuring the intensity of theinfrared light that is totally reflected by the first face; and (i-C) astep of obtaining the first infrared absorption spectrum by irradiatinginfrared light of a predetermined wave number onto a second face of thetest piece that was first exposed when the test piece was sampled, andmeasuring the intensity of the infrared light that is totally reflectedby the second face.
 4. The plastic identifying method according to claim1, wherein the predetermined group of materials is a group of materialsthat contains at least one material selected from the group consistingof acrylonitrile-butadiene-styrene copolymers, polypropylenes, andpolystyrenes.
 5. The plastic identifying method according to claim 1,wherein the predetermined group of materials is a group of materialscontaining plastics that contain flame retardants.
 6. The plasticidentifying method according to claim 5, wherein the plastics thatcontain flame retardants are acrylonitrile-butadiene-styrene copolymersthat contain tetrabromobisphenol A series flame retardants.
 7. Theplastic identifying method according to claim 5, wherein the plasticsthat contain flame retardants are polystyrenes that contain at least oneof the flame retardants selected from the group consisting ofdecabrominated flame retardants, tetrabromobisphenol A series flameretardants, triazine series flame retardants, and ethylenebis seriesflame retardants.
 8. The plastic identifying method according to claim1, wherein the item to be identified is identified as anacrylonitrile-butadiene-styrene copolymer in the step (ii) when: thefirst infrared absorption spectrum has a peak in the wave number rangeof 906 cm⁻¹ to 914 cm⁻¹, the wave number range of 1,023 cm⁻¹ to 1,031cm⁻¹, and the wave number range of 2,234 cm⁻¹ to 2,242 cm⁻¹; and thevalue obtained by dividing the highest peak intensity in the wave numberrange of 1,000 cm⁻¹ to 1,008 cm⁻¹ by the highest peak intensity in thewave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹ is not greater than 0.5.9. The plastic identifying method according to claim 1, wherein the itemto be identified is identified as a polypropylene in the step (ii) when:the first infrared absorption spectrum has a peak in the wave numberrange of 1,373 cm⁻¹ to 1,381 cm⁻¹, the wave number range of 2,913 cm⁻¹to 2,921 cm⁻¹, and the wave number range of 2,946 cm⁻¹ to 2,954 cm⁻¹.10. The plastic identifying method according to claim 1, wherein theitem to be identified is identified as a polystyrene that does notcontain a tetrabromobisphenol A series flame retardant in the step (ii)when: the first infrared absorption spectrum has a peak in the wavenumber range of 1,368 cm⁻¹ to 1,376 cm⁻¹ and the wave number range of1,023 cm⁻¹ to 1,031 cm⁻¹; and the value obtained by dividing theintensity of the highest peak in the wave number range of 1,000 cm⁻¹ to1,008 cm⁻¹ by the intensity of the highest peak in the wave number rangeof 1,023 cm⁻¹ to 1,031 cm⁻¹ is not greater than 0.5.
 11. The plasticidentifying method according to claim 1, wherein the item to beidentified is identified as a polystyrene that does not contain a flameretardant in the step (ii) when: the first infrared absorption spectrumhas a peak in the wave number range of 1,368 cm⁻¹ to 1,376 cm⁻¹ and thewave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹; and does not have a peakin the wave number range of 1,348 cm⁻¹ to 1,356 cm⁻¹; and the valueobtained by dividing the intensity of the highest peak in the wavenumber range of 1,000cm⁻¹ to 1,008 cm⁻¹ by the intensity of the highestpeak in the wave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹ is not greaterthan 0.5.
 12. The plastic identifying method according to claim 1,wherein the item to be identified is identified as a polystyrene thatcontains decabrominated flame retardant in the step (ii) when: the firstinfrared absorption spectrum has a peak in the wave number range of1,349 cm⁻¹ to 1,357 cm⁻¹ and the wave number range of 1,023 cm⁻¹ to1,031 cm⁻¹; and does not have a peak in the wave number range of 907cm⁻¹ to 915 cm⁻¹; and the value obtained by dividing the intensity ofthe highest peak in the wave number range of 1,000 cm⁻¹ to 1,008 cm⁻¹ bythe intensity of the highest peak in the wave number range of 1,023 cm⁻¹to 1,031 cm⁻¹ is not greater than 0.5.
 13. The plastic identifyingmethod according to claim 1, wherein the item to be identified isidentified as a polystyrene that contains a tetrabromobisphenol A seriesflame retardant in the step (ii) when: the first infrared absorptionspectrum has a peak in the wave number range of 1,000 cm⁻¹ to 1,008 cm⁻¹and the wave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹; and the valueobtained by dividing the intensity of the highest peak in the wavenumber range of 1,000 cm⁻¹ to 1,008 cm⁻¹ by the intensity of the highestpeak in the wave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹ is at least0.5.
 14. The plastic identifying method according to claim 1, whereinthe item to be identified is identified as a polystyrene that contains atriazine series flame retardant in the step (ii) when: the firstinfrared absorption spectrum has a peak in the wave number range of1,356 cm⁻¹ to 1,364 cm⁻¹, the wave number range of 1,227 cm⁻¹ to 1,235cm⁻¹, the wave number range of 1,085 cm⁻¹ to 1,093 cm⁻¹, and the wavenumber range of 1,023 cm⁻¹ to 1,031 cm⁻¹; and the value obtained bydividing the intensity of the highest peak in the wave number range of1,000 cm⁻¹ to 1,008 cm⁻¹ by the intensity of the highest peak in thewave number range of 1,023 cm⁻¹ to 1,031 cm⁻¹ is not greater than 0.5.15. The plastic identifying method according to claim 1, wherein theitem to be identified is identified as a polystyrene that contains anethylenebis series flame retardant in the step (ii) when: the firstspectrum has a peak in the wave number range of 1,369 cm⁻¹ to 1,377cm⁻¹, the wave number range of 1,137 cm⁻¹ to 1,145 cm⁻¹, the wave numberrange of 742 cm⁻¹ to 750 cm⁻¹, and the wave number range of 1,023 cm⁻¹to 1,031 cm⁻¹; and the value obtained by dividing the intensity of thehighest peak in the wave number range of 1,000 cm⁻¹ to 1,008 cm⁻¹ by theintensity of the highest peak in the wave number range of 1,023 cm⁻¹ to1,031 cm⁻¹ is not greater than 0.5.
 16. The plastic identifying methodaccording to claim 1, that, after the step (ii), further comprises: (x)a step of obtaining a third infrared absorption spectrum by excludingfrom the peaks of the first infrared absorption spectrum the peaks ofthe infrared absorption spectrum of any plastic identified as containedin the item to be identified; and (y) a step of identifying a substancethat is adhering to a surface of the item to be identified by matchingthe third infrared absorption spectrum with the group of infraredabsorption spectra.
 17. The plastic identifying method according toclaim 16, wherein the adhering substance is at least one materialselected from the group consisting of fats/oils, proteins, coatings,celluloses, and inorganic silicates.
 18. The plastic identifying methodaccording to claim 16, wherein, in the step (y), the adhering substanceis identified as at least one material selected from the groupconsisting of fats/oils and coatings when: the third infrared absorptionspectrum has a peak in the wave number range of 1,736 cm⁻¹ to 1,744cm⁻¹.
 19. The plastic identifying method according to claim 16, wherein,in the step (y), the adhering substance is identified as a protein when:the third infrared absorption spectrum has a peak in the wave numberrange of 1,646 cm⁻¹ to 1,654 cm⁻¹ and the wave number range of 1,541cm⁻¹ to 1,549 cm⁻¹.
 20. The plastic identifying method according toclaim 16, wherein, in the step (y), the adhering substance is identifiedas at least one of the group consisting of celluloses and inorganicsilicates when: the third infrared absorption spectrum has a peak in thewave number range of 1,000 cm⁻¹ to 1,100 cm⁻¹.
 21. The plasticidentifying method according to claim 3, that, after the step (i),further comprises: (X) a step of obtaining a fourth infrared absorptionspectrum by excluding the peaks of the first infrared absorptionspectrum from the peaks of the second infrared absorption spectrum, and(Y) a step of identifying a substance that is adhering to a surface ofthe item to be identified by matching the fourth infrared absorptionspectrum with the group of infrared absorption spectra.
 22. The plasticidentifying method according to claim 3, that, after the step (i),further comprises: (s) a step of determining an area D₁ of the peaks inthe first infrared absorption spectrum in the wave number range of 400cm⁻¹ to 7,000 cm⁻¹; (t) a step of determining an area D₂ of the peaks inthe second infrared absorption spectrum in the wave number range of 400cm⁻¹ to 7,000 cm⁻¹; and (u) a step of determining a value D by dividingthe area D₂ by the area D₁.
 23. The plastic identifying method accordingto claim 1, that, after the step (ii), further comprises: (S) a step ofestablishing a first baseline of the first infrared absorption spectrumby joining with a straight line a peak in the first infrared absorptionspectrum in the vicinity of the wave number 2,750 cm⁻¹ with a peak inthe vicinity of the wave number 3,140 cm⁻¹; (T) a step of establishing asecond baseline of the first infrared absorption spectrum by joiningwith a straight line a peak in the first infrared absorption spectrum inthe vicinity of the wave number 3,663 cm⁻¹ with a peak in the vicinityof the wave number 3,791 cm⁻¹; and (U) a step of taking the peakintensity in the first infrared absorption spectrum in the vicinity ofthe wave number 2,920 cm⁻¹ as H₁ and the peak intensity in the vicinityof the wave number 3,750 cm⁻¹ as H₂, and determining a value H bydividing the H₂ by the H₁; wherein the H₁ is the peak intensity of thefirst infrared absorption spectrum relative to the first baseline, andthe H₂ is the peak intensity of the first infrared absorption spectrumrelative to the second baseline.